Multi-flute ball end mill

Abstract

A multi-flute ball end mill of the present invention includes: a shank portion configured to rotate about a rotational axis; a cutting edge portion; three or more ball edges formed on the cutting edge portion; gashes formed between the ball edges; peripheral cutting edges continuous with end portions of the ball edges on the shank portion side; and flutes formed between the peripheral cutting edges continuously with the gashes. The degree of curvature of the ball edges is 35% to 55%. Each of the gashes includes four faces of a rake face of each of the ball edges, a gash wall face, a first gash face, and a second gash face. The second gash face is formed such that the closer the second gash face is to the rotation center point, the more inwardly the second gash face enters a second face of each of the ball edges.

The invention claimed is: 
     
       1. A multi-flute ball end mill, comprising:
 a shank portion configured to rotate about a rotational axis; 
 a cutting edge portion having a ball edge portion at a tip thereof; 
 three or more ball edges formed on the ball edge portion of the cutting edge portion; 
 three or more gashes formed between the respective ball edges; 
 three or more peripheral cutting edges continuous with end portions of the ball edges on the shank portion side; and 
 three or more flutes formed between the respective peripheral cutting edges continuously with the respective gashes, 
 wherein a degree of curvature of each of the ball edges is 35% to 55%, the degree being a ratio of a length of a perpendicular line drawn from an apex of a convex curved line of each of the ball edges to a line segment connecting a rotation center point that is an intersection point between the rotational axis and the cutting edge portion with a terminal point of each of the ball edges on the shank portion side with respect to a length of the line segment, 
 wherein each of the gashes includes four faces of a rake face of each of the ball edges, a gash wall face, a first gash face, and a second gash face, the four faces being continuous in a rotational direction of the multi-flute ball end mill, and 
 wherein the second gash face is formed such that the closer the second gash face is to the rotation center point, the more inwardly the second gash face enters a second face of each of the ball edges continuous with a back side of each of the ball edges in the rotational direction. 
 
     
     
       2. The multi-flute ball end mill according to  claim 1 ,
 wherein, in a case where the multi-flute ball end mill is seen from the tip side thereof, when a circle P centered on the rotation center point O with a diameter of 0.03D to 0.2D where D is the diameter of the cutting edge portion and passing through the gashes is drawn, 
 the second face of each of the ball edges and the second gash face are continuous in this order on a back side of each of the ball edges in the rotational direction on the circumference of the circle P; and 
 a ratio of a length of a circular arc P 1 -P 3  with respect to a length of a circular arc P 1 -P 2  is 3.5 to 6.0, the circular arc P 1 -P 3  being formed by intersection points P 1  and P 3  where a first ball edge and a second ball edge adjacent to each other intersect with the circle P, and the circular arc P 1 -P 2  being formed by the intersection point P 1  and an intersection point P 2  that is located on the circumference of the circle P and forms a boundary between the second face of the first ball edge and the second gash face. 
 
     
     
       3. The multi-flute ball end mill according to  claim 1 ,
 wherein, in a case where the multi-flute ball end mill is seen from the tip side thereof, when a circle S centered on the rotation center point O with a diameter of 0.4D to 0.6D where D is the diameter of the cutting edge portion and passing through the gashes is drawn, 
 the second face of each of the ball edges, a third face of each of the ball edges, and the gash wall face are continuous in this order on a back side of each of the ball edges in the rotational direction on the circumference of the circle S; and 
 a ratio of a length of a circular arc S 1 -S 3  with respect to a length of a circular arc S 1 -S 2  is 2.1 to 3.3, the circular arc S 1 -S 3  being formed by intersection points S 1  and S 3  where a first ball edge and a second ball edge adjacent to each other intersect with the circle S, and the circular arc S 1 -S 2  being formed by the intersection point S 1  and an intersection point S 2  that is located on the circumference of the circle S and forms a boundary between the third face of the first ball edge and the gash wall face. 
 
     
     
       4. The multi-flute ball end mill according to  claim 1 ,
 wherein at a position apart from the rotation center point toward the shank portion in a direction of the rotational axis by 0.15D where D is the diameter of the cutting edge portion, 
 a radial rake angle of each of the ball edges is −29° to −11°; and 
 a rake angle of each of the peripheral cutting edges is −9° to −1°. 
 
     
     
       5. The multi-flute ball end mill according to  claim 2 ,
 wherein, in a case where the multi-flute ball end mill is seen from the tip side thereof, when a circle S centered on the rotation center point O with a diameter of 0.4D to 0.6D where D is the diameter of the cutting edge portion and passing through the gashes is drawn, 
 the second face of each of the ball edges, a third face of each of the ball edges, and the gash wall face are continuous in this order on a back side of each of the ball edges in the rotational direction on the circumference of the circle S; and 
 a ratio of a length of a circular arc S 1 -S 3  with respect to a length of a circular arc S 1 -S 2  is 2.1 to 3.3, the circular arc S 1 -S 3  being formed by intersection points S 1  and S 3  where a first ball edge and a second ball edge adjacent to each other intersect with the circle S, and the circular arc S 1 -S 2  being formed by the intersection point S 1  and an intersection point S 2  that is located on the circumference of the circle S and forms a boundary between the third face of the first ball edge and the gash wall face. 
 
     
     
       6. The multi-flute ball end mill according to  claim 2 ,
 wherein at a position apart from the rotation center point toward the shank portion in a direction of the rotational axis by 0.15D where D is the diameter of the cutting edge portion, 
 a radial rake angle of each of the ball edges is −29° to −11°; and 
 a rake angle of each of the peripheral cutting edges is −9° to −1°. 
 
     
     
       7. The multi-flute ball end mill according to  claim 3 ,
 wherein at a position apart from the rotation center point toward the shank portion in a direction of the rotational axis by 0.15D where D is the diameter of the cutting edge portion, 
 a radial rake angle of each of the ball edges is −29° to −11°; and 
 a rake angle of each of the peripheral cutting edges is −9° to −1°. 
 
     
     
       8. The multi-flute ball end mill according to  claim 5 ,
 wherein at a position apart from the rotation center point toward the shank portion in a direction of the rotational axis by 0.15D where D is the diameter of the cutting edge portion, 
 a radial rake angle of each of the ball edges is −29° to −11°; and 
 a rake angle of each of the peripheral cutting edges is −9° to −1°.